Using the accurate expression of the Voigt profile we obtained,a method for the calculation of the optical depth of laser produced plasma is given out. Taking the magnesium laser produced plasma as an example,the optical depth,and the escape probability of magnesium laser produced plasma based on the optical depth are calculated,and the calculation results are in agreed with the experimental results. Finally,we point out a method to calculate the resonance escape factor of laser produced plasma using the optical depth.